<!DOCTYPE html>
<html lang="en">
  <head>
    <meta charset="UTF-8" />
    <meta http-equiv="X-UA-Compatible" content="IE=edge" />
    <meta name="viewport" content="width=device-width, initial-scale=1.0" />
    <title>Document</title>
    <style>
      #result {
        width: 200px;
        height: 200px;
        border: 1px solid purple;
      }
    </style>
  </head>
  <body>
    <div id="result"></div>

    <script>
      const result = document.getElementById("result");

      result.addEventListener("mouseover", function () {
        //1.创建对象
        const xhr = new XMLHttpRequest();

        //2.初始化，设置请求类型和url路径
        xhr.open("POST", "http://127.0.0.1:8000/server");

        //这里我们来设置一个请求头的信息
        xhr.setRequestHeader(
          "Content-Type",
          "application/x-www-form-urlencoded"
        );
        //这里设置了请求体的内容是字符串类型

        //3.发送请求到服务器
        xhr.send("a=100&b=100");

        //4.事件绑定处理服务端返回的结果
        xhr.onreadystatechange = function () {
          if (xhr.readyState == 4) {
            if ((xhr.status >= 200) & (xhr.status < 300)) {
              result.innerHTML = xhr.response;
            }
          }
        };
      });
    </script>
  </body>
</html>
